I had this very problem a while back, and several people suggested doing multiple renders then merging the results, which worked for me. My image had Michael 3, The Freak, two copies of the Dragon, and the Cyclorama from DAZ in it, along with a lot of props, poseable and otherwise. I rendered it three times, once with only the Mike figure and his props visible, once with the Freak visible only, and once with the dragons visible. I left the Cyclorama on in all three renders. I took the resulting image and imported them into Paint Shop Pro as separate layers, then erased the parts of the background obscuring the characters, and it worked great.

The total render time was about 45 minutes, and it took about half an hour to get the image assembled the way I wanted it.

Another possibility would be to export the scene to something else and render it there, if you have other software. I've taken very complex scenes (in excess of 50 million polygons) and rendered them successfully in POV-Ray. It's a gold-plated, cast iron, B-word to export Poser content to POV, though. If you've got Bryce and the DAZ import plug-in, that's pretty easy, or you might just try rendering your scene with DAZ|Studio (since there's currently no cost other than the learning curve and disk space for it) and see how that works.

Hope that's helpful,
Jack